The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a technique which can be effectively used for the manufacturing of high frequency power amplifier which is mainly comprised of hetero junction bipolar transistors (HBT) which constitute ultrahigh-speed IC elements.
As a semiconductor device which exhibits high speed performance and low power consumption performance, a hetero junction bipolar transistor (hereinafter also referred to as HBT) has been known. This hetero junction bipolar transistor is used in a form that the transistor is incorporated into a high frequency power amplifier (RF power amplifying module) of a mobile communication terminal such as a portable cellular phone.
The HBT has a structure in which a sub-collector layer and a collector layer are sequentially laminated onto one surface (main surface) of a semiconductor substrate, a base layer is partially formed over the collector layer, and an emitter layer which is formed of a semiconductor having a wide band gap is partially formed over the base layer.
In a power amplifying device for transmission in a communication system, the HBT has now been used as a transistor. Such a semiconductor device is described in Japanese Laid-open Patent 210723/2001.
In Japanese Laid-open Patent 210723/2001, a technique for manufacturing a semiconductor device having a bias circuit which suppresses a change of an idle current attributed to a temperature change of a power transistor Tr1 is disclosed. Such a semiconductor device is manufactured using a GaAs substrate as a base and, for compensating for a temperature shift of the idle current, a plurality of Schottky diodes are provided to a base inputting part. The bias circuit is constituted of two transistors (Tr2, Tr3) which are connected to the power transistor Tr1, two Schottky diodes (D1, D2) and three resisters (R1 to R3).
That is, a base terminal of the power transistor Tr1 is connected to a collector terminal of the transistor Tr2 through a resistor R3 in an emitter follower method, and a base terminal of the transistor Tr2 is grounded through the transistor Tr3 which short-circuits a base and a collector of the Schottky diodes D1, D2 thus suppressing the change of the idle current C of the transistor Tr1 which is generated when the temperature changes.
Further, with respect to this semiconductor device, base electrodes and the Schottky electrodes of the HBT are simultaneously formed at the time of manufacturing the semiconductor device.
On the other hand, in the manufacturing of the HBT, for preventing an excessive etching of the sub-collector layer, there has been known a technique which provides an InGaP layer between the sub-collector layer and the collector layer. This technique is described in IEEE Electron Device Lett., vol. 18, p355, 1997.
Further, in IEEE Electron Device Lett., vol. 18, p559, 1997, there is disclosed a technique which enhances the isolation performance by arranging an undoped InGaP layer having a resistance higher than a resistance of an undoped GaAs layer below a collector layer.